To meet the ever increasing worldwide demand for crude oil, new reserves have been discovered and exploited at various undersea locations. Development of equipment and methods for finding, drilling, producing, and locating these undersea reserves is expected to continue as the more accessible continental reserves become exhausted.
Once an undersea reserve has been located by any of the known methods, it is necessary to drill one or more production wells. Typically, a plurality of production wells, closely spaced to one another, are drilled from a suitable surface vessel and are thereafter capped. Sometime later, or in lieu of capping the production wells, the crude oil flowing from the wells is combined and joined to a pipeline which extends to an onshore storage facility. Alternatively, the flows are combined into a riser which extends to the surface. From the onshore storage facility or from the offshore riser, the crude oil is loaded on to transportation vessels such as tankers or the like.
A drawback associated with piping the crude oil collected from the production wells to an onshore storage facility is that as exploration moves further from shore, the laying of a suitable pipeline becomes more expensive, based not only upon the overall length of the pipeline, but also upon the underwater terrain which may be encountered. In instances where production wells are drilled in deep waters, on the order of 5000 feet, the laying of a suitable pipeline may become economically or physically unfeasible.
Where the alternate method of combining the flows from the production wells to a riser is used, other drawbacks are encountered. As is often the case, the combined flows from the production wells may be at insufficient flow rates to quickly fill the transportation vessel which is moored on station. The problems of loading the tanker are aggravated in foul weather where quick loading and unhooking from the riser are of utmost importance. Furthermore, the riser may present a hazard to shipping or result in a possible oil spill should a vessel encounter the riser.
Accordingly, it can be appreciated that there is a need for an offshore oil storage and transfer facility which is adapted to receive and store crude oil from one or several production wells and, on demand, unload to quickly fill the transportation vessel. The storage facility should be economical to construct and locate, should be safe against oil spills, and should not present an obstruction to shipping. Furthermore, the storage facility should be simple to use, including means for delivering the crude oil, which may include means not requiring pumps.